Exhaust gas purifying device for engine

ABSTRACT

An exhaust gas purifying device for an engine according to the present invention includes a NOx absorbing catalytic converter provided in an exhaust path of the engine, an exhaust light oil adding injector which supplies a reducing agent component into the exhaust path, a control unit which executes the rich spike operation that controls an air-fuel ratio to the rich side per predetermined time, which adds the HC component to the NOx absorbing catalytic converter, and which heats to an S purge temperature or higher so as to eliminate a sulfur component absorbed by the NOx absorbing catalytic converter, and a catalyst temperature measuring sensor which measures the temperature of the NOx absorbing catalytic converter, wherein the control unit controls an operation cycle of the rich spike operation based on the deviation of the S purge temperature with respect to the temperature measured by the catalyst temperature measuring sensor.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2004-107807, filed Mar. 31, 2004, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an exhaust gas purifying device for an engine having an exhaust emission purifying function which purifies hazardous components included in the exhaust emission of an internal combustion engine, and particularly, it relates to a catalyst temperature rise control at the time of an S purge drive.

2. Description of the Related Art

Conventionally, an exhaust gas purifying device provided with a NOx absorbing catalytic converter in an exhaust pipe of an engine is known. According to the exhaust gas purifying device using such a NOx catalyst, a rich spike of lowering an excess air ratio of the gas provided into the catalytic converter (hereinafter referred to as “before catalyst λ”) to 1 or less by supplying a reducing agent such as light oil on an exhaust emission upstream side of a NOx reduction catalytic converter in order to discharge and reduce the absorbed NOx needs to be carried out regularly (for example, once a minute). Specifically, the rich spike is carried out by lowering λ by controlling an engine intake system, post jetting, or the like as well as by jetting the fuel to the exhaust pipe on the upstream side of the catalytic converter.

Moreover, a technique of changing a lean combustion degree and a rich combustion degree according to the catalyst temperature in the case of executing the rich spike is known (for example, see Jpn. Pat. Appln. KOKAI Publication No. 11-270382).

On the other hand, according to the NOx absorbing catalyst, sulfur poisoning is generated due to a sulfur component in the fuel. For the elimination of the sulfur, a discharging S purge drive to eliminate the sulfur component should be carried out for about 1 minute regularly (for example, once per 5,000 km travel distance). For the S purge drive, for example a catalyst temperature of 600° C. or higher (an S purge temperature) is needed. Therefore, a technique of raising the NOx absorbing catalyst temperature by supplying HC by adding the light oil in an exhaust pipe, post jetting, or the like is known (for example, see Jpn. Pat. Appln. KOKAI Publication No. 11-270382).

According to the above-mentioned exhaust gas purifying device for an engine, the following problems arise. The graphs H1 to H4 of FIG. 6 are graphs showing the change according to the time passage of the timing of a rich spike signal to execute a rich spike operation in the exhaust gas purifying device, the timing of an S purge signal to execute the S purge drive, a CO, HC supply amount to be supplied into the exhaust pipe and the catalyst temperature (the catalytic converter outlet gas temperature).

As it is observed from the graphs H1 and H2, since a rich spike control and an S purge control are executed independently, the rich spike operation and the S purge drive may be executed at the same time. Since both the rich spike operation and the S purge drive are executed by the HC supply by the exhaust light oil addition or the post jetting, the HC supply to the catalyst can be excessive depending on the timing so that the excessive temperature rise of the catalyst can be generated.

Therefore, although preventive measures against the HC supply excess by reducing the CO, HC supply amount at the time of the S purge drive is conceivable, on the contrary, a problem arises in that the time for reaching the S purge temperature is prolonged or the S purge temperature cannot be attained.

BRIEF SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide an exhaust gas purifying device for an engine, capable of efficiently executing a rich spike control and an S purge drive and preventing an excessive temperature rise of a catalyst according to a rich spike operation.

The present invention provides an exhaust gas purifying device for an engine, comprising: a catalytic converter provided in an exhaust path of the engine which absorbs NOx in the exhaust gas flowing into the exhaust path and reduces the NOx when an air-fuel ratio of the exhaust gas becomes rich; a reducing agent supply unit which supplies a reducing agent component including HC into the exhaust path; a rich spike control unit which executes a rich spike operation that controls the air-fuel ratio temporarily to the rich side by operating the reducing agent supply unit per predetermined time period; an S purge control unit which judges whether or not an S purge drive that adds the HC component to the catalytic converter and eliminates a sulfur component absorbed in the catalytic converter by heating to a predetermined temperature or higher is needed; and a catalyst temperature measuring sensor which measures the temperature of the catalytic converter, wherein the rich spike control unit controls a operation cycle of the rich spike operation based on the deviation of the predetermined temperature with respect to the temperature measured by the catalyst temperature measuring sensor in the case where the S purge is judged to be necessary by the S purge control unit.

The present invention also provides an exhaust gas purifying device for an engine, comprising: a catalytic converter provided in an exhaust path of the engine which absorbs NOx in the exhaust gas flowing into the exhaust path and reduces the NOx when an air-fuel ratio of the exhaust gas becomes rich; a reducing agent supply unit which supplies a reducing agent component including HC into the exhaust path; a rich spike control unit which executes a rich spike operation that controls the air-fuel ratio temporarily to the rich side by operating the reducing agent supply unit per predetermined time period; an S purge control unit which judges whether or not an S purge drive that adds the HC component to the catalytic converter and eliminates a sulfur component absorbed in the catalytic converter by heating to a predetermined temperature or higher is needed; and a catalyst temperature measuring sensor which measures the temperature of the catalytic converter, wherein the rich spike control unit controls an operation period of the rich spike operation based on the deviation of the predetermined temperature with respect to the temperature measured by the catalyst temperature measuring sensor in the case where the S purge is judged to be necessary by the S purge control unit.

According to the present invention, the rich spike control and the S purge drive can be executed efficiently and the excessive temperature rise of the catalyst according to the rich spike operation can be prevented.

Additional advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention, and together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the invention.

FIG. 1 is a block diagram showing the configuration of an exhaust gas purifying device for an engine according to an embodiment of the present invention;

FIG. 2 is a graph showing the relationship between a CO, HC supply amount per unit time and a catalyst temperature;

FIG. 3 is a graph showing the relationship between a rich spike cycle and a rich spike period, and the CO, HC supply amount per unit time;

FIG. 4 is an explanatory graph showing the change according to the time passage of the timing of a rich spike signal in the exhaust gas purifying device for an engine, the timing of an S purge signal to execute the S purge drive, the CO, HC supply amount supplied into an exhaust gas piping, and a catalyst temperature (a catalytic converter outlet gas temperature);

FIG. 5 is an explanatory graph showing the change according to the time passage of the timing of the rich spike signal in the exhaust gas purifying device for an engine, the timing of the S purge signal to execute the S purge drive, the CO, HC supply amount supplied into the exhaust gas piping, and the catalyst temperature (the catalytic converter outlet gas temperature); and

FIG. 6 is an explanatory graph showing the change according to the time passage of the timing of the rich spike signal in a conventional exhaust gas purifying device, the timing of the S purge signal to execute the S purge drive, the CO, HC supply amount supplied into the exhaust gas piping, and the catalyst temperature (the catalytic converter outlet gas temperature).

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a diagram showing the configuration of an exhaust gas purifying device for an engine 10 according to an embodiment of the present invention.

An engine system 10 comprises a diesel engine 20. The diesel engine 20 is connected to an intake pipe 30 on an intake side thereof and to an exhaust pipe 40 on an exhaust side thereof. Furthermore, the exhaust side of the diesel engine 20 and the intake pipe 30 are connected by an EGR piping 50 which circulates the exhaust gas (EGR gas) to the intake pipe 30. The reference numeral 60 in FIG. 3 denotes a supercharger and the reference numeral 100 denotes a control unit.

The intake pipe 30 is provided with an air flow sensor 30, a compressor 61 of the supercharger 60, an inter cooler 32, an intake throttle 33, and a connection part 34 with respect to the EGR piping 50, in that order from the intake side.

The exhaust pipe 40 is provided with a turbine 62 of the supercharger 60, an exhaust light oil adding injector 41 which supplies the light oil into the exhaust pipe 40, and a NOx absorbing catalytic converter 42, in that order from the diesel engine 20 sides. The NOx absorbing catalytic converter 42 absorbs the NOx in the exhaust gas flowing into the exhaust pipe 40 and reduces the absorbed NOx at the time the exhaust gas becomes rich.

The EGR piping 50 is provided with an EGR cooler 51 which cools down the exhaust gas, and an EGR valve 52 which adjusts the exhaust gas flow amount, in that order form the exhaust pipe 40 sides.

The control unit 100 is connected to an output of a catalyst temperature measuring sensor 101 disposed on an outlet side of the NOx absorbing catalytic converter 42 of the exhaust pipe 40 such that the catalyst temperature of the NOx absorbing catalytic converter 42 is always fed back.

According to the engine system 10 configured as above, the S purge drive is executed by the following operation. That is, during the ordinary engine drive, the rich spike operation is executed by a predetermined interval by the combustion control of the engine and the addition of a light oil including the HC from the exhaust light oil adding injector 41 into the exhaust pipe 40. At the time, if there is a command of the S purge drive, the temperature of the NOx absorbing catalytic converter 42 is raised by supplying the HC from the exhaust light oil adding injector 41 into the exhaust pipe 40. At the time, in the case where the catalyst temperature does not reach an S purge temperature T, the rich spike operation is controlled such that the temperature rise speed is made higher, that is, the cycle of the rich spike operation (M in FIG. 4) is shortened.

In the case where the catalyst temperature reaches the S purge temperature T, the interval of the rich spike operation is returned to the original interval. Thereby, the catalyst temperature fluctuates around the S purge temperature T without having the excessive temperature rise. In the case where the catalyst temperature is higher than the S purge temperature T, the rich spike cycle may be controlled so as to be made longer. At the time the S purge drive is finished so as to return to the ordinary engine drive, the rich spike operation is returned to the ordinary cycle.

As mentioned above, according to the engine system 10 of this embodiment, when the S purge drive is started, the HC supply is increased by shortening the rich spike cycle according to the increase of the deviation of the catalyst temperature with respect to the S purge temperature T so as to control the catalyst temperature such that it reaches the S purge temperature T in a short time. As it can be observed from FIGS. 2 and 3, this denotes that the catalyst temperature rise amount can consequently be made larger by shortening the rich spike cycle so as to increase the CO, HC supply amount per unit time. Therefore, while executing the rich spike, the sulfur component absorbed by the NOx absorbing catalytic converter 42 can be eliminated smoothly by the S purge drive as well as the excessive temperature rise can be prevented.

The graphs L1 to L4 of FIG. 5 are graphs showing the change according to the time passage of the timing of a rich spike signal to execute a rich spike operation in an exhaust gas purifying device for an engine according to a modified embodiment of the engine system 10, the timing of an S purge signal to execute an S purge drive, a CO, HC supply amount supplied into an exhaust gas piping, and a catalyst temperature (a catalytic converter outlet gas temperature).

Although the cycle of the rich spike operation is adjusted in the embodiment mentioned above, in this embodiment a rich spike period (time for executing the rich spike per one time) is adjusted. That is, the rich spike operation is executed by a predetermined interval for a certain period during the ordinary engine drive. At the time, when there is a command for the S purge drive, the temperature of a NOx absorbing catalytic converter 42 is raised by supplying the HC in an exhaust pipe 40. At the time, in the case where the catalyst temperature has not reached an S purge temperature T, the rich spike operation is controlled such that the temperature rise speed is made higher, that is, the period of the rich spike operation (N in FIG. 5) is prolonged.

When the catalyst temperature reaches the S purge temperature T, the rich spike period returns to the original length. Thereby, the catalyst temperature fluctuates around the S purge temperature T without having the excessive temperature rise. In the case where the catalyst temperature is higher than the S purge temperature T, the rich spike period may be controlled so as to be made shorter. At the time the S purge drive is finished so as to return to the ordinary engine drive, the rich spike period is returned to the ordinary length. Also in this modified embodiment, the same effect as in the case of controlling the rich spike cycle as mentioned above can be obtained.

The present invention is not limited to the above-mentioned embodiments. For example, although either the rich spike cycle or the rich spike period is controlled in the embodiments mentioned above, they may be controlled at the same time. Naturally various modifications can be executed without departing from the scope of the gist of the present invention.

Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents. 

1. An exhaust gas purifying device for an engine, comprising: a catalytic converter provided in an exhaust path of the engine which absorbs NOx in the exhaust gas flowing into the exhaust path and reduces the NOx when an air-fuel ratio of the exhaust gas becomes rich; a reducing agent supply unit which supplies a reducing agent component including HC into the exhaust path; a rich spike control unit which executes a rich spike operation that controls the air-fuel ratio temporarily to the rich side by operating the reducing agent supply unit per predetermined time period; an S purge control unit which judges whether or not an S purge drive that adds the HC component to the catalytic converter and eliminates a sulfur component absorbed in the catalytic converter by heating to a predetermined temperature or higher is needed; and a catalyst temperature measuring sensor which measures the temperature of the catalytic converter, wherein the rich spike control unit controls a operation cycle of the rich spike operation based on the deviation of the predetermined temperature with respect to the temperature measured by the catalyst temperature measuring sensor in the case where the S purge is judged to be necessary by the S purge control unit.
 2. The exhaust gas purifying device for an engine according to claim 1, wherein the cycle is made shorter as the deviation is increased.
 3. An exhaust gas purifying device for an engine, comprising: a catalytic converter provided in an exhaust path of the engine which absorbs NOx in the exhaust gas flowing into the exhaust path and reduces the NOx when an air-fuel ratio of the exhaust gas becomes rich; a reducing agent supply unit which supplies a reducing agent component including HC into the exhaust path; a rich spike control unit which executes a rich spike operation that controls the air-fuel ratio temporarily to the rich side by operating the reducing agent supply unit per predetermined time period; an S purge control unit which judges whether or not an S purge drive that adds the HC component to the catalytic converter and eliminates a sulfur component absorbed in the catalytic converter by heating to a predetermined temperature or higher is needed; and a catalyst temperature measuring sensor which measures the temperature of the catalytic converter, wherein the rich spike control unit controls an operation period of the rich spike operation based on the deviation of the predetermined temperature with respect to the temperature measured by the catalyst temperature measuring sensor in the case where the S purge is judged to be necessary by the S purge control unit.
 4. The exhaust gas purifying device for an engine according to claim 3, wherein the period is made longer as of the deviation is increased. 